The present invention relates to a device for regulating and cleaning an air port (3) arranged in a wall (2) of a furnace, especially a soda house furnace, comprising a cleaning arrangement (1), which in it turn comprises a cleaning member (7) movable with respect to the walls of the air port (3), and arrangement (4) for regulating the air flow through the air port (3), and air casing (5) being arranged around the air port (3) on the outer side of the furnace wall (2), a drum (12) being arranged inside the air casing (5) and connected to a wall (13) of the air casing (5) located opposite to the furnace wall (2), the cleaning arrangement (1) being also connected to the wall (13) of the air casing (5) and extending at least partially through the drum (12), the regulating arrangement having a cover member (14) movable with respect to the drum (12), the cleaning member (7) being movable between two end positions and independently of the position of the cover member (14), and the cleaning member (7) being in a first of the end positions located at least partially inside the furnace and a second of the end positions at least partially outside the furnace.
Such devices are used within the field of soda house furnaces and the like, in which the wall is provided with a plurality of air ports, the air flow of which has to be regulated and which sometimes have to be cleaned.
Within the cellulose industry the spent liquors from paper wood boiling (sulphate spent liquor and in some case sulphite spent liquor) are combusted for recovery in a recovery boiler. The nature of the fuel and the process conditions result in a tendency of plugging of the openings, through which combustion air is supplied, usually called air ports, through dust particles and flowing cinder products. These pluggings are more accentuated in the lower region of the air port and especially at the bottom thereof. There are different arrangements of cleaning members reciprocating in the air ports for cleaning thereof and which are activated upon need or periodically. It is important from the environmental point of view to achieve such a complete combustion as possible of the spent liquor located in the recovery boiler. The supply of air is an important parameter for this purpose. A regulating device is arranged for regulating the air supply through an air port. There are according to the prior art a number of examples of regulating devices and cleaning devices for furnace air ports.
According to a first example of the prior art the cleaning member has a sleeve shape and has also a task to regulate the air flow, which is achieved by the fact that the sleeve has a cross section having a shape and size corresponding to the air port, in which the air flow present in a slit between the cleaning member and the air port, which as such has a cleaning effect, is dependent upon how far the cleaning member is introduced into the air port in the resting position thereof. Such a device has the advantage that air will be supplied without any control, or at least intermittently during the cleaning operation.
According to a further example of the prior art the cleaning member has only a cleaning function, and a throttle is arranged for regulating the air supply. The throttle is here arranged on the outer side of the furnace wall close to the air port and may for example be constituted by a lid being moveable downwardly for covering the air port. When cleaning of the air port is to take place the lid has accordingly to be removed from the position thereof covering the air port at least partially, so that the cleaning member may be introduced into the air port. An uncontrolled flow of air into the air port during the cleaning thereof also takes place in this example.
According to a further example of the prior art, the cleaning device is at least partially enclosed in a drum, which extends from a wall located opposite to the furnace wall and belonging to an air casing arranged outside the airport, said drum extending from said wall in the direction towards the air port. The cleaning device is of a conventional type and comprises a cleaning member, a holding element and a power member, in which the cleaning member is arranged at one end of the holding element, said holding element being at a second and thereof actively connected to the power member, in which the cleaning member is moveable in a reciprocating movement with respect to the air port for cleaning the walls thereof. A sleeve is moveable along the length of the drum at an end thereof facing the air port. Said sleeve having an inner cross section shape corresponding to the outer cross section shape of the drum so as to seal around the drum and an at least somewhat larger cross section than the air port for also being able so seal therearound. By such a design the cleaning member may be brought to and fro through the air port while the sleeve is arranged in a position causing a suitable air flow to the air port. The air will then flow through a circumferential slot formed between the sleeve and the furnace wall located around the air port. As a consequence of the flow of non-combustible material and cinder products along an inner wall of the furnace and the tendency thereof to cause pluggings of the air port this may also reach the circumferential slot and at least partially plug it. Upon such a partially plugging of the slot air will flow in through the air port through portions of the slot not plugged, which on one hand results in a reduction of the controllability of the air flowing through the air port since changes of the position of the sleeve with respect to the air have to be carried out with increasing degree of plugging, and on the other the non-combustible material reaching the slot may immobilise the sleeve or at least create a resistance against movement thereof. The plugging of the air port will primarily take place at the bottom of the air port, since the flowing non-combustible material is collected on the bottom, which means that the immobilisation of the sleeve tends to take place of the portion of the sleeve intended to cover the bottom of the air port. As a consequence of the fact that the opening formed for the air flow is slot-like a comparatively short movement of the sleeve will result in a comparatively large change of the area of the opening, which means that a device with a high accuracy for the movement of the sleeve is required for obtaining a change desired of the amount of air flowing into the furnace per time unit.
The object of the present invention is to provide a device for regulating and cleaning an air port arranged in the wall of a furnace, which eliminates at least some of the drawbacks mentioned above in regulating and cleaning an air port according the conventional technique.
This object is according to the device according to the invention obtained by arranging the cover member for regulating the air flow through at least an opening defined by at least a lateral wall of the drum and having a restricted extension in the circumferential direction of the drum. By the fact that the at least one opening has a restricted extension in the circumferential direction of the drum the opening will not have any circumferential slot character, so that the problems defined above of an opening with a slot-shape are eliminated.
According to an embodiment, in which the cover member has at least a wall portion for at least partially cover the opening on movement of the cover member and where the cover member is movable substantially in the longitudinal direction of the opening, it is possible to make the shape of the effective open area of the opening almost point-like, in which the air flowing through the opening and further into through the air port may have a substantially jet-like character. Such an air jet means a higher degree of concentrated air amount with respect to the character of the air flowing in through a slot-like opening according to the prior art, which involves a number of advantages. Firstly, it will be easier to check and regulate the air flow into the furnace, and an air flow into the furnace being turbulent to a smaller extent is achieved due to the air jet, which in its turn means that the air flowing in may reach further into the furnace and may by that in a higher degree prevent particles incompletely combusted to flow up from the melt in a centre region of the furnace.
According to another embodiment of the invention, in which at least a portion of the opening is arranged on the level with a bottom of the air port, the air supply will in a higher degree take place along this bottom, which in its turn means that a clean flushing of cinder products from this bottom being stronger than in the prior art is achieved.
According to another embodiment of the invention, which constitutes a further development of the preceding embodiment, an end of the drum facing the air port is at least partially arranged at a distance from the furnace wall delimiting the air port, and an upper and a lower wall part having an extension in the transversal direction of the drum substantially corresponding to the width of the drum is adapted to connect the drum at the top and at the bottom, respectively, with the air port, which means that two openings oppositely located are formed in the transversal direction of the drum and between the furnace wall delimiting the air port, a lateral wall arranged in the transversal direction of the drum and said wall parts, respectively, and by the fact that the cover member has two substantially parallel wall portions which are arranged at a mutual distance substantially corresponding to the width of the drum. The cover member will upon a movement in parallel with the furnace wall delimiting the air port more or less cover the openings formed between the surface wall delimiting the air port, the lateral walls of the drum and said wall parts. This means that the cover member in a rest position allowing air supply through the openings is arranged at a distance from the bottom of the air port, and it is counteracted that the cover member gets stuck by possible cinder products gathered on the bottom of the air port.